physiological/power basis of KOPS

[gabbard]

Is there any research related to power output versus knee location? Local biomechanics guru Andy Pruitt of the Boulder Center for Sports Medicine consistently espouses the idea that the front of your knee should coincide with the front of the crank arm, (which roughly puts the underside of the patella at about the spindle) for a basic starting point for minimal knee pain and optimal power. Ned Overend has said the same thing in one of his training books, although this is related to mountain bikes, with the caveat that you move the seat back for emphasizing climbing. I know others that seem to want a 72 degree seat tube angle, setback seat post, and jam the seat all the way back.

I'm going to contact Pruitt about this also, but wanted to see what others thought.

Steve, bored in Colorado with a new frame that he can't ride because there is 8" of snow on the ground

P.S. This is really esoterica and more of academic interest, because the easiest way for me to increase my power would be to train more.

[Ti Designs]

Where the knee falls over the pedal spindle is a point of reference, nothing more. It's become one of those "rules of thumb" which I spend countless hours trying to get people to see past. Almost as bad as people picking a stem based on where they see the front hub... People will be quick to point out that when the cranks are at 3:00 and 9:00 you have the greatest mechanical advantage pushing straight down, and if this were an internal combustion engine with the piston directly over the crank shaft I might agree. In cycling we have two major muscle groups producing most of the force, the glutes which extend the leg down from the hips, and the quads which extend the leg out from the knee. Optimal positioning on the bike must make the best use of both of those muscle groups. When the pedals are at 3:00 and 9:00 the quads can't do anything to deliver power to the wheel - so much for KOPS...

Two other things to look at: First, what people think they are telling their muscles and the message the muscles get are two different things. Most people see a hill and think "I need to push harder". What they do is push longer, which has them pushing past the bottom of the pedal stroke which is all wasted energy. In moving the saddle back, the range of contraction of the glutes (the largest muscle group in the action) is reached sooner in the pedal stroke, which brings what the brain says and what the legs do back in line. Second, there is the whole issue of where the upper body weight is placed. Setback and angel at the hips is what puts the upper body weight onto the pedals where it belongs and takes it off the handlebars. I keep going back to the analogy of sitting in a chair with your feet in front of you. You can pivot at the hips and lean forward and you don't fall on your face - your body weight is supported on you feet. Same thing happens on a bike, with your feet in front of you, your body weight is supported on the pedals (free power!). I use where the knee is over the pedal as a point of measurment, but I look at where the riders center of gravity is in relationship to the pedals to set fore/aft position.

[gabbard]

First, anything I say below is not meant to contradict you - you have obviously done this a bunch, so I am looking for clarification:

One thing that I did not understand is the 3:00-9:00 analogy - it seems like your glutes can produce a force here, but your response seems to imply that you can not produce any usable force - can you explain?

"Optimal positioning on the bike must make the best use of both of those muscle groups. When the pedals are at 3:00 and 9:00 the can't do anything to deliver power to the wheel - so much for KOPS..."

When you fit a person, are you fitting for handling (COG) first and the assumption is that the body will adapt to change its highest efficiency power band? What about the effects of the lever arm of the leg at 3:00/9:00. Isn't the lever arm the shortest when the knee is effectively over the pedal spindle? If you can generate X force at the knee, the force transmitted to the pedal will be a function of the total lever arm to the pedal, measured from the hip, wouldn't it?

By moving the saddle back, are you increasing the range over which the glutes contract, giving you more power over the stroke, and how much do you really increase the stroke if you move the saddle back 1 cm? 1-2% for a person with 90 cm inseam? Could this be accomplished by a saddle farther forward with longer cranks?

Maybe I should experiment with a saddle farther back...

Steve

[vaxn8r]

Thanks ti...I always enjoy reading your stuff. I came to my position from racing back in the 80's and finding what gave me the most power. Very few tweaks since then because I'm so comfortable. Once you hit "fit Nirvana" why change it? Still, I like reading the theory on why a certain fit works especially without the "cookie cutter" ideas on KOP and hub obscured by bars if arms relaxed, slightly bent, looing forward...yadda yadda yadda).

[Needs Help]

Keith Bontrager's take on the subject:

"The Myth of Kops"
http://www.sheldonbrown.com/kops.html

[Kane]

Actually, the ideal position varies with the person. The ideal is easily established with a riding computer that measures power at the crank. If you are on one of those machines you can experiment and find your ideal position.

[hypnospin]

this may well be the best indicator, but if one has adapted to a position that may be less than optimum, and could actualy produce more output over time with a position change, this variable would then not be identified.

trends come and go. it was once thought necessary to have a crit specific bike to race crits, one feature of which would be a knee forward position. thought to be good for widing up and all...lemond did advocate bucking this trend.

then there is the tri position which has slammed the knee forward for these specific bikes.

with the advent of mtb, the saddle went waay back, and this is now carrying over to road. a ripple effect. witness the prerequisite ++setback posts in vogue.

things always seem to gravitate back to neutral, aka kops.

a comparison of tibia and fibula length may be a factor here. turns out my thighs are proportionately longer.

for myself, i have found that rearward of this kops is an advantage, giving what i feel is more leverage and muscle involvement of the glutes, hams 'n erectors.

may affect spin but technique developed over time can offset this.

i also have my cleats towards the front of the shoes which i also feel provides more leverage.

true, neutral positioning is just a guideline but it provides a starting point reference from which to begin setup.

Actually, the ideal position varies with the person. The ideal is easily established with a riding computer that measures power at the crank. If you are on one of those machines you can experiment and find your ideal position.

[Ti Designs]

Gabbard,

There was a lack of proof reading on my part which is why part of my post didn't make much sense.



One thing that I did not understand is the 3:00-9:00 analogy - it seems like your glutes can produce a force here, but your response seems to imply that you can not produce any usable force - can you explain?

Yeh, I left out the word quads - which can only extend your leg forward from the knee, so if your knee is directly over the pedal spindle (or even close) the quads do nothing. Use of the quads has to do with saddle to pedal position over the top, not at 3:00 and 9:00 - KOPS only looks at one factor.


When you fit a person, are you fitting for handling (COG) first and the assumption is that the body will adapt to change its highest efficiency power band?

Not exactly. Center of gravity is part of the leverage on the pedals. One of the things I work with people in changing their position is how they support their upper body. If the center of gravity falls over the pedals the weight can be supported on the forward pedal - that's what I call free power, taking the force that was supported by the handlebar and putting it into driving the pedals. From that standpoint, fore/aft position has as much to do with torso length and position as it does with the knee.


By moving the saddle back, are you increasing the range over which the glutes contract, giving you more power over the stroke, and how much do you really increase the stroke if you move the saddle back 1 cm? 1-2% for a person with 90 cm inseam? Could this be accomplished by a saddle farther forward with longer cranks?

It is increasing the range, but it's as much a timing thing with most riders. I couldn't say what kind of percent gain there is in range (well, I could given all the details, but that's not the point), my goal here is to decrease wasted energy by shifting the effort earlier and teaching riders to start using their hamstrings to pull back, which also signals the end of the use of the glutes. As for longer crank arms, there is something to be said for a wider circle producing a longer range of individual muscle usage, but we also need to offset that with greater fatigue over time and a reduced rance of RPMs.

[hypnospin]

so as for your longer crankarm statement,
what about the guy who rides a 52 frame with 170's

(bring to mind any sprinters we have known?),

his crank length is proportionately longer than the majority who would take this "fatigue and rpm"
stance seriously and ride their 172.5's, never realizing they do not see the light.

please keep riding the shorter cranks, i silently ask of those with whom i ride.



Gabbard,

There was a lack of proof reading on my part which is why part of my post didn't make much sense.





. As for longer crank arms, there is something to be said for a wider circle producing a longer range of individual muscle usage, but we also need to offset that with greater fatigue over time and a reduced rance of RPMs.